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Kidney failure is a growing problem in the older population. Data on people reaching end-stage kidney disease (ESKD) is collected by the U.S. Renal Data System (USRDS). All dialysis units that receive funding from Medicare are required to file data with the USRDS, so that nationwide data are available on over 95% of people receiving renal replacement therapy. Information published in the 2006 USRDS annual data report shows that approximately 1.5 in 1000 persons aged 65 years or older are initiating treatment for ESKD each year—the highest rate of any age group. Over the last 10 years, the number of older people enrolling for treatment has increased by 41% in the group of people aged 75 years or older and by 48% in the 80+-year-old age group. Almost 4 in 1000 persons are currently maintained on renal replacement therapy, with the 75+-year-old age group growing at 10% per year. The peak incidence for ESKD is the 70- to 74-year-old age group, while the peak prevalence falls in the 65- to 69-year-old age group. In contrast, the incidence of ESKD in the 20- to 44-year-old age group has remained flat over the last 10 years, with only 6% growth in the 45- to 64-year-old group. Although some of the increase in renal replacement therapy for the older population indicates a greater willingness to offer treatment to older individuals, much of the increase is owing to people surviving to experience the chronic changes that occur with aging. The kidney undergoes significant age-related change. Other common diseases such as hypertension and diabetes accelerate these changes.

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Aging in the kidney is characterized by changes of both structure and function. It must be emphasized that many of the aging studies have been performed on laboratory animals, particularly rodents, that demonstrate quite different patterns of aging from humans. For example, kidney weight increases throughout life in rats while kidney mass and size in humans peaks in the fourth decade and declines thereafter. Care should be taken when reading the literature to keep in mind that changes seen in animal models may not be reflected by parallel changes in humans. Historical data from human postmortems describing changes in the kidney made no effort to exclude patients with kidney disease or significant comorbidities. More recently data on aging has been developed from longitudinal studies, such as the Baltimore Longitudinal Aging Study, in which the medical histories of the study volunteers are well documented. There are also data accumulating from the kidney transplant population. Older living donors are increasingly being used and are put thorough a rigorous medical workup for renal function and comorbid conditions before being accepted as donors. This has allowed acquisition of data on normal aging in the kidney, uncomplicated by the presence of medical comorbidities. Aging in the kidney is generally characterized by spontaneous progressive decline in renal function accompanied by thickening of the basement membrane, mesangial expansion, and focal glomerulosclerosis.

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Functional Changes

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